1. Field of the Invention
The present invention relates to a circuit breaker for interrupting an electric circuit for a short time.
2. Description of the Related Art
In an electrical component system provided in a vehicle, when something is wrong with a load of a power window, a wire harness, or the like, constituted by a plurality of electric wires connecting a battery and various loads, a high-current fuse inserted between the battery and the wire harness is blown out to interrupt a connection between the battery and the wire harness, thereby preventing the loads, the wire harness, and the like from being burnt and damaged.
However, in the case of the electric component system using such a high-current fuse, even if something is wrong with the load of the power window, the wire harness, or the like connecting the battery and various loads, the fuse does not blow out unless a current exceeds a tolerated value which is previously set for the high-current fuse. Therefore, various protecting apparatuses have been developed. When a high-current close to the tolerated value is continuously flowing, the protecting apparatus detects the current and interrupts the connection between the battery and the wire harness.
FIG. 1 is a sectional view showing one example of the protecting apparatus using a bimetal. The protecting apparatus shown in FIG. 1 is made of insulation resin, and comprises a housing 103 formed at its upper portion with a fuse accommodating portion 102, a lid 113 for closing the fuse accommodating portion 102 such that the latter can be opened and closed, a power source terminal 105 disposed in a lower portion in the housing 103 such that an upper end of the power source terminal 105 projects into the fuse accommodating portion 102 and a lower end thereof is exposed outside, and the exposed portion of the power source terminal 105 being connected to a positive terminal of a battery 104, a load terminal 109 disposed in a lower portion in the housing 103 such that an upper end of the load terminal 109 projects into the fuse accommodating portion 102 and a lower end thereof is exposed outside, and the exposed portion of the load terminal 109 being connected to a load 108 through an electric wire 107 constituting a wire harness 106, a fusible member 110 made of low-melting metal and having one end connected to an upper end of the power source terminal 105 and the other end connected to an upper end of the load terminal 109, an intermediate terminal 111 disposed in a lower portion in the housing 103 such that the intermediate terminal 111 is located at an intermediate position between the power source terminal 105 and the load terminal 109 and a lower end of the intermediate terminal 111 is exposed outside, and the exposed portion being connected to a negative terminal of the battery 104, and a bimetal 112 which is made of a long plate-like member comprising two kinds of metal bonded together and which is disposed such as to be opposed to the fusible member 110 such that a lower end of the bimetal 112 is connected to an upper end of the intermediate terminal Ill and an upper end thereof being bent into an L-shape.
When an ignition switch and the like of the vehicle are operated, and a current is flowing through a path comprising the positive terminal of the battery 104, the power source terminal 105, the fusible member 110, the load terminal 109, the electric wire 107 of the wire harness 106, the load 108, and the negative terminal of the battery 104, and when an abnormal condition occurs in the load 108 or in the wire harness 106 connecting the load 108 and a protecting apparatus 101, and a current equal to or greater than the tolerated value flows through the fusible member 110, the fusible member 110 is heated and blown out for protecting the load 108, the wire harness 106 and the like.
Further, even if something is wrong with the load 108 or the wire harness 106 connecting the load 108 and the protecting apparatus 101, and a large current flows through the fusible member 110, if the current does not exceed the tolerated value, the fusible member 110 is heated by the current flowing through the latter and the bimetal 112 starts deforming. When a predetermined time is elapsed from the instance when the large current starts flowing through the fusible member 110, a tip end of the bimetal 112 comes into contact with the fusible member 110, and a large short-circuit current flows through the fusible member 110 in a path comprising the positive terminal of the battery 104, the power source terminal 105, the fusible member 110, the intermediate terminal 111, and the negative terminal of the battery 104, and the latter is blown out.
With the above structure, even when a current equal to or lower than the tolerated value flows for a preset time or longer, the circuit is interrupted to protect the wire harness 106 and the load 108.
As another protecting apparatus 101 rather than this protecting apparatus, a protecting apparatus 121 has also developed.
The protecting apparatus 121 shown in FIG. 2 comprises a housing 122 made of insulation resin, a power source terminal 124 embedded in one side surface of the housing 122 and having a lower end connected to a positive terminal of a battery 123, and a load terminal 128 embedded in the other side surface of the housing 122 and having a lower end connected to a load 127 through an electric wire 126 constituting a wire harness 125. The protecting apparatus 121 further comprises an electric wire 131 including a fusible lead 129 which is made of low-melting metal and formed into U-shape and a heat-proof coating 130 formed such as to cover the fusible lead 129. The protecting apparatus 121 further comprises a coil 132. The coil 132 is made of shape-memory alloy which is formed into a shape wound around the electric wire 131 as shown in FIG. 2 when it is in a martensite phase state, and which is formed into its original phase shape fastening the electric wire 131. The protecting apparatus 121 further comprises an external terminal 133 whose upper end is connected to one end of the coil 132 and whose lower end is connected to a negative terminal of the battery 123.
When an ignition switch and the like of the vehicle are operated, and a current is flowing through a path comprising the positive terminal of the battery 123, the power source terminal 124, the fusible lead 129 of the electric wire 131, the load terminal 128, the electric wire 126 of the wire harness 125, the load 127 and the negative terminal of the battery 123, and when an abnormal condition occurs in the load 127 or in the wire harness 125 connecting the load 127 and a protecting apparatus 121, and a current equal to or greater than the tolerated value flows through the fusible lead 129, the fusible lead 129 is heated and blown out for protecting the load 127, the wire harness 125 and the like.
Further, even if something is wrong with the load 127 or the wire harness 125 connecting the load 127 and the protecting apparatus 121, and a large current flows through the fusible lead 129, if the current does not exceed the tolerated value, the fusible lead 129 is heated by the current flowing through the latter and a temperature of the coil 132 rises. When a predetermined time is elapsed from the instant when the large current starts flowing through the fusible lead 129, and the temperature of the coil 132 rises to 120xc2x0 C. to 170xc2x0 C., the coil 132 changes from its martensite phase state to its original phase and bites into the heat-proof coating 130 which is softened by heat and comes into contact with the fusible lead 129, and a large short-circuit current flows through the fusible lead 129 in a path comprising the positive terminal of the battery 123, the power source terminal 124, the fusible lead 129, the coil 132, the external terminal 133, and the negative terminal of the battery 123, and the latter is blown out.
With the above structure, even when a current equal to or lower than the tolerated value flows for a preset time or longer, the circuit is interrupted to protect the wire harness 125 and the load 127.
However, in the above-described conventional protecting apparatuses 101 and 121, there are problems as follows.
First, in the case of the protecting apparatus shown in FIG. 1, it is detected whether a large current flows through the fusible member 110 using the bimetal 112 made of two kinds of metals having different thermal expansion coefficients and bonded to each other. Therefore, if the magnitude of the current flowing through the fusible member 110, the bimetal 112 is deformed, and the time that elapsed before the circuit is interrupted is varied.
Thus, when a failure that a large current flows intermittently occurs, a temperature of the fusible member 110 does not rise more than a certain value, and there is an adverse possibility that the wire harness 106 or the load 108 may be burnt before the protecting apparatus 101 interrupts the circuit.
In the case of the protecting apparatus 121 shown in FIG. 2, it is detected whether a large current flows through the fusible lead 129 using the coil 132 made of shape-memory alloy. Therefore, if the magnitude of the current flowing through the fusible lead 129, the coil 132 is deformed, and the time that elapsed before the circuit is interrupted is varied.
Thus, when a failure that a large current flows intermittently occurs, a temperature of the fusible lead 129 does not rise more than a certain value, and there is an adverse possibility that the wire harness 125 or the load 127 may be burnt before the protecting apparatus 121 interrupts the circuit.
Further, in the protecting apparatuses shown in FIGS. 1 and 2, the heat reaction time of the bimetal 112 or the coil 132 which is a thermal-deformable electrical conduction member is varied depending upon the current flowing therethrough. Further, the heat reaction of the thermal-deformable electrical conduction member is not operated timely when an abnormal condition occurs.
It is an object of the present invention to provide a circuit breaker capable of reliably interrupting a circuit in a short time to protect an electrical part when an abnormal signal of a vehicle is input.
To achieve the above object, according to a first aspect of the present invention, there is provided a circuit breaker comprising a heating portion disposed between a first connecting terminal and a second connecting terminal, the heating portion being in contact with the first connecting terminal and the second connecting terminal and having electric conductivity and charged with a heating agent, an igniting portion for igniting the heating agent charged in the heating portion, an outer case in which the igniting portion and the heating portion are accommodated, an extendable resilient member, and a removable member for mounting the resilient member in its compressed state, the removable member being capable of being attached to and detached from the outer case, and being disposed in the vicinity or in contact with the heating portion when the removable member is mounted to the outer case.
According to the first aspect, the removable member which mounts the extendable resilient ember is disposed in the vicinity of or in contact with the heating portion when the removable member is mounted to the outer case. When the igniting portion is ignited by the signal indicative of the abnormal condition sent from outside, the heating agent charged in the heating portion is heated, and the removable member is melted by the heat. The compressed resilient member is stretched to jump up the heating portion and therefore, the electric connection between the heating portion and the first and second connecting terminals is interrupted. Therefore, it is possible to reliably interrupt the electric circuit of the vehicle within a short time, and to protect electrical parts.
Further, since the removable member is attachable to and detachable from the outer case, the removable member can easily be attached to and detached from the outer case. Further, the resilient member is held by the removable member and thus, no external force is applied to the connected portion between the first and second connecting terminals and the heating portion.
According to a second aspect of the invention, the outer case comprises an upper case and a lower case put on the upper case, the lower case being formed with an opening and a groove, and the removable member to which the resilient member is mounted has a case mounting claw which is fitted to the groove, and is formed such that the removable member can be inserted into the opening.
According to the second aspect, the removable member can easily be mounted to the lower case by inserting the removable member to which the resilient member is mounted into the opening formed in the lower case, and by fitting the case mounting claw formed on the removable member into the groove formed in the lower case. Therefore, it is possible to easily assemble the entire apparatus.
According to a third aspect of the invention, the removable member comprises a base, a belly which is embedded with respect to the base and around which the resilient member is wound, a locking portion formed on an end of the belly for locking the resilient member in its compressed state, and the case mounting claw.
According to the third aspect, the resilient member is wound around the belly by bending the locking portion inwardly and pushing the resilient member into the belly through the locking portion, and the resilient member is locked by the locking portion in its compressed state. That is, since the locking portion is disposed inside the resilient member, the locking portion comes into strong contact with the heating portion, and the heat conductivity becomes excellent. Further, the resilient member is held by the removable member, no external force is applied to the connected portion between the first and second connecting terminals and the heating portion.
According to a fourth aspect of the invention, the locking portion is made of a low-melting metal or resin member which is melted by a heat of the heating agent.
According to the fourth aspect, since the locking portion is made of a low-melting metal or resin member which is melted by a heat of the heating agent, the locking portion is melted by the heat of the heating agent, the resilient member is stretched, the heating portion jumps up, and the electric connection between the first and second connecting terminals is interrupted.
According to a fifth aspect of the invention, an end of the heating portion is formed with a side wall, the side wall and tip ends of the first connecting terminal and the second connecting terminal are connected to each other through low-melting material.
According to the fifth aspect, since the side wall and tip ends of the first connecting terminal and the second connecting terminal are connected to each other through low-melting material, if the removable member and the low-melting material are melted by the heat of the heating agent, the heating portion jumps up, and the electric connection between the first and second connecting terminals is interrupted. Therefore, it is possible to reliably interrupt the electric circuit of the vehicle within a short time, and to protect electrical parts. Further, no spring force is applied to the low-melting material which is the connected portion between the first and second connecting terminals and the heating portion, it is possible to enhance the reliability of the connected portion.